Alhydrogel TM , a widely used adjuvant, modulates multiple networks implicated in brain aging and has potential in the prevention of age-related cognitive decline

BACKGROUND: A preliminary efficacy trial in early Alzheimer’s Disease (AD) serendipitously revealed that Alhydrogel ^® (alum) treated controls showed preservation of cognition, function, and hippocampal volume, with early onset and striking effect size. Aging is the highest risk factor for developing AD. We propose repurposing Alhydrogel ^® , formulated as AD04™, as a novel prophylactic strategy for age-related decline of brain function, supported by the established safety record of Alhydrogel ^® as a potent adjuvant and immunomodulator for licensed human vaccines and allergy immunotherapies. Aging is associated with decreased cognitive function, neurogenesis, proliferation, and synapse density, with increased neuroinflammation. Hence, aged mice enable investigation of relevant neuropathology and were utilized here in a study of hippocampal behavioral and proteomics to examine the potential mode of action of AD04™ in the aged brain. Aged (24 months) C57BL/6 mice were injected subcutaneously with AD04™ or PBS three times at two-week intervals. Memory was assessed 3 - 5 days after the final injection using contextual and cue fear conditioning. Next day, hippocampi were collected and analyzed via unbiased proteomics and lipidomics, with young mice as controls. Approximately 7,000 gene products were analyzed. RESULTS: AD04 ^TM improved freezing behavior in contextual tests indicative of enhanced hippocampal-dependent memory. AD04™ modulated hippocampal proteins involved in lipid metabolism (fatty acid biosynthesis, bile acid biosynthesis, glycerolipid metabolism), including regulators of lipid droplet homeostasis (which are critical to microglial function), APP processing, Wnt/β-catenin signaling, and autophagy/membrane trafficking, as well as elevating levels of ceramides and cerebrosides. CONCLUSIONS: Peripherally administered AD04™ in aged mice induces improvements in hippocampus/amygdala dependent behavior, and pleiotropic modulation of proteins across multiple networks. These experimental findings align with clinical observations and strongly support further studies of AD04™ mouse models of age-related diseases including AD.